Winter storms, higher payroll taxes, tax refund delays and China's bird flu scare were just a few of the factors working against restaurants in the first three months of 2013. But you wouldn't have known it from the customers crowding into chains like Chipotle Mexican Grill (CMG), Starbucks (SBUX) and Panera Bread (PNRA). The same holds true for investors, who crowded into restaurant stocks, despite a slew of reports out in the past week showing